1. FIELD OF THE INVENTION
This invention relates to a method of recovering waste paper and, specifically, to a method of producing a recovered pulp which is stained to only a slight extent and has an excellent brightness by subjecting waste paper of a pressure sensitive copying paper to defibration processing with an alkaline solution containing a surface active agent.
2. DESCRIPTION OF THE PRIOR ART
Pressure sensitive copying papers usually include those papers comprising an upper paper having micro capsules containing an electron donative color former dissolved in an organic solvent applied on the surface of the sheet, a lower paper with an electron attractive clay applied on the surface of the sheet and an intermediate paper having capsules containing a color former applied to one surface of the sheet and having a clay applied to the other surface of the sheet, or those having micro capsules and a clay applied on the same side of the sheet. Such pressure sensitive copying papers are described in, for example, U.S. Pat. Nos. 2,505,470; 2,505,489; 2,550,471; 2,548,366; 2,712,507; 2,730,456; 2,730,457; 2,939,009; 3,427,180; 3,455,721; 3,516,845; 3,634,121; and 3,672,935; German OLS No. 1,939,624; or in A. Kondo, Microcapsule, Nikkan Kogyo Shimbun Co., Tokyo 1970.
In using pressure sensitive papers by the combination of an upper paper and a lower paper or by the combination of an upper paper, an intermediate paper or papers and a lower paper, when pressure is locally applied to a capsule-containing layer and a clay-containing layer in contact with each other, the capsules in the pressurized area are ruptured and a color is produced by the reaction of the color former and the clay. Also, a color is produced by the application of a localized pressure to a pressure sensitive paper having capsules and a clay on the same side of the sheet.
Various types of conventional defibrating machines for regenerating waste paper such as a pulper, a beater, a high-speed defibrating machine, a disc refiner or a conical refiner are known, and they are used alone or in combination. Usual waste paper can be easily defibrated in these defibrating machines, but auxiliaries are required for a waste paper which is relatively difficult to defibrate such as a wet-proof paper. Various alkaline chemicals and aluminum sulfate and the like are often used as auxiliaries.
When waste paper is defibrated using the conventional method, capsules are destroyed during the defibration because of the mechanical grinding action exerted on them, and the exposed color former and clay react to product color. Therefore, the color occurs in the pulp recovered according to the conventional method and the pulp is remarkably stained. Such a pulp can not be used as a raw material for high quality paper and only a part of the pulp has been used exclusively as a raw material for low quality paper.